Muffler for small engine

ABSTRACT

A muffler for a small engine includes a first expansion chamber  12  for exhaust gas having an exhaust gas inlet  11  being connected to an exhaust gas outlet of the engine, a second expansion chamber  15  being partitioned from the first expansion chamber  12  by a partition plate  14  and being communicated with the first expansion chamber  12  through a first communicating hole  13  on the partition plate  14 , and a third expansion chamber  18  being partitioned from the second expansion chamber  15  by the partition plate  14  and being communicated with the second expansion chamber  15  through a second communicating hole  16  on the partition plate  14  and having an exhaust gas outlet  17 . A first heat resistant mesh catalyst  19  is disposed on the exhaust gas inlet  11 . A first exhaust gas purifier  20  composed of a heat resistant knit fabric  20   a  coated with a catalyst for purifying the exhaust gas is disposed on the communicating hole  13  on the partition plate  14.    
     Accordingly, the muffler for a small engine having a large muffling effect and a large purification effect on the exhaust gas can be provided. A manufacturing process of the exhaust gas purifier is simple and thereby a manufacturing cost of the muffler for a small engine is reduced.

TECHNICAL FIELD

The present invention relates to a muffler for a small engine suited foruse in a brush cutter or a chain saw, for example.

BACKGROUND ART

A conventional muffler for a small engine comprises, as shown in FIG.21, an exhaust gas first expansion chamber 2 having an exhaust gas inlet1 connected to an exhaust gas outlet of the engine, and an exhaust gassecond expansion chamber 4 having an exhaust gas outlet 3. Between thefirst expansion chamber 2 and the second expansion chamber 4, forexample, an exhaust gas purifier 5 made of a honeycomb-like stainlesssteel support body having innumerable small holes along an axialdirection and coated with a catalyst such as Rhodium, Palladium, etc.,is disposed.

Further, a conventional muffler for a small engine comprises, as shownin FIG. 22, an exhaust gas first expansion chamber 2 having an exhaustgas inlet 1 connected to an exhaust gas outlet of the engine and anexhaust gas second expansion chamber 4 having an exhaust gas outlet 3. Aconcave exhaust gas receiver 6 having a plurality of communicating holes6 b on a concave surface 6 a which is disposed in the first expansionchamber 2 so that the concave surface 6 a faces to the exhaust gas inlet1. Between the first expansion chamber and the second expansion chamber,an exhaust gas purifier 5 made of a honeycomb-like stainless steelsupport body having innumerable small holes in an axial direction andcoated with the catalyst for purifying the exhaust gas. In FIG. 21 andFIG. 22, numerals ‘2 a’, ‘4 a’ and ‘7’ indicate a wall which forms thefirst expansion chamber 2, a wall which forms the second expansionchamber 4 and a partition plate which partitions the first expansionchamber 2 and the second expansion chamber 4, respectively.

Conventionally, various kinds of mufflers for small engines have beendeveloped. For example, a catalyst carrier for such a muffler is made bylaminating thin metal sheets each having a number of openings with eachsurface of a cloth catalyst, and the catalyst carrier is formed into awaveform shape and the plate side is disposed in parallel with a flowdirection of exhaust gas (Patent document 1).

A conventional exhaust gas muffler as described hereunder is known. Theexhaust gas muffler accommodates a cylindrical shaped cloth catalysthaving a coarsely woven and a cylindrical shaped cloth catalyst having afinely woven, therein. Each cylindrical shaped cloth catalyst iscomparatively soft, is made by coating a catalyst onto a fabric and isformed into a cylindrical shape having an oval cross-section. Thecoarsely woven cylindrical shaped catalyst is disposed on an upperportion of the exhaust gas muffler so as to surround two reinforcingbeams, and an exhaust gas outlet of an engine is communicated with aninside of the coarsely woven cylindrical shaped catalyst through anopening of the exhaust gas muffler. The finely woven cylindrical shapedcatalyst is disposed at a lower portion of the exhaust gas muffler so asto surround two reinforcing beams, and so that a portion of an outersurface of the finely woven cylindrical shaped catalyst contact closelywith an inner wall surface of the exhaust gas muffler. Accordingly, theinside of the exhaust gas muffler is partitioned to a chamber inside thecoarsely woven cylindrical shaped catalyst, a chamber outside thecoarsely woven cylindrical shaped catalyst, a chamber inside the finelywoven cylindrical shaped catalyst and a chamber in a lowermost portionoutside the finely woven cylindrical shaped catalyst. (Patent document2)

Another conventional exhaust gas muffler as described hereunder isknown. In the exhaust gas muffler, a plurality of catalyst carriers areconnected in series in a flow passage of exhaust gas. Each catalystcarrier is stacked with a support plate having an opening and is coveredwith a wire mesh. One of the catalyst carrier stacked with a supportplate is fixed to an upper housing of the exhaust gas mufflerapproximately horizontally. The other catalyst carrier stacked with asupport plate is fixed to a lower housing of the exhaust gas mufflerapproximately horizontally. The exhaust gas muffler is partitioned tothree chambers by the support plates. The wire mesh of the catalystcarrier being at an exhaust gas inlet side has a coarse opening and thewire mesh of the catalyst carrier being at an exhaust gas outlet sidehas a fine opening. (Patent document 3)

Another conventional exhaust gas muffler as described hereunder isknown. An exhaust gas muffler of an internal-combustion engine includesa box-like exhaust gas muffler in which an inner exhaust gas mufflerpart and an outer exhaust gas muffler part are detached with each otheror integrated; a communicating hole which is disposed in the exhaust gasmuffler and introduces exhaust gas being generated in theinternal-combustion engine to an inside of the exhaust gas muffler; anda tube member composed of a reticulated material having a properelasticity being provided with a catalyst thereto. The tube member isdisposed in a space in the exhaust gas muffler so that a barrel of thetube is held in such a direction as being clipped between the exhaustgas muffler parts. According to the above mentioned exhaust gas mufflerstructure, only if the tube member is disposed in the space between theexhaust gas muffler parts when the inner and the outer exhaust gasmuffler parts are integrated, the tube member is retained so as to fitwith a surrounding configuration by barrel of the tube elasticallydeforming freely. (Patent document 4)

Another conventional exhaust gas muffler as described hereunder isknown. A cylindrical spark arrestor which is means for preventing sparksfrom splashing is composed of a cylindrical wire mesh member. Thecylindrical spark arrestor is retained in a state being fixed between anend of a tail pipe and an inner surface of an attaching body of theexhaust gas muffler. (Patent document 5)

Another conventional exhaust gas muffler as described hereunder isknown. A partition plate is disposed along an axial direction of acylinder of an engine in an exhaust gas muffler, and an inside of theexhaust gas muffler is partitioned into a first chamber near to anengine body and a second chamber distant from an engine body. A catalystis kept in a lower portion of the partition plate. The catalyst having afunction of re-burning unburned gas in exhaust gas through oxidationreaction, is constituted by coating the catalyst to a surface of apassage in a honeycomb structure composed of a stainless steel. An innercatalyst cover which is disposed on a position in the first chamber andcovers about one half inner side portion of the catalyst and an outercatalyst cover which is disposed on a position in the second chamber andcovers about one half outer side portion of the catalyst, are attachedto the partition plate. A space surrounded by the inner catalyst coverand the partition plate is a first catalyst chamber. An inlet sidecommunicating hole which communicates the first catalyst chamber withthe first chamber is formed on the inner catalyst cover. A spacesurrounded by the outer catalyst cover and the partition plate is asecond catalyst chamber. An outlet side communicating hole whichcommunicates the second catalyst chamber with the second chamber isformed on the outer catalyst cover. A catalyst installing box in whichthe catalyst is installed is configured by attaching the inner catalystcover and the outer catalyst cover to the partition plate. (Patentdocument 6)

Another conventional exhaust gas muffler as described hereunder isknown. An exhaust gas muffler is provided with an expansion chamber intowhich exhaust gas being blown from an exhaust gas outlet of an internalcombustion engine is introduced. A peripheral part of the expansionchamber comprises a double wall structure composing an inner wall paneland an outer wall panel being isolated with a distance so as to form aspace between the panels. An inlet of the exhaust gas which introducesthe exhaust gas in the expansion chamber into the space is formed on theinner wall panel, an outlet of the exhaust gas which exhausts theexhaust gas from the space to an outside is formed on the outer wallpanel, and a spark arrestor screen is disposed so as to cover the outletof the exhaust gas. A cylindrical oxidation catalyst composed of a metalcarrier is disposed as an exhaust gas purifier so as to protrude in eachof the first expansion chamber and the second expansion chamber. (Patentdocument 7)

Another conventional catalyst muffler as described hereunder is known. Acatalyst muffler is divided into a body housing and a lid housing. Eachof a ceramic cloth, a cloth catalyst and a wire mesh made of a stainlesssteel is formed so as to adjust closely to the three-dimensionalconfiguration of each housing, and the ceramic cloth, the cloth catalystand the wire mesh made of the stainless steel are stacked in turn andjoined to the whole the inner surface of each housing. (Patent document8)

A conventional muffler as described hereunder is known. Ageneral-purpose muffler for an internal combustion engine is made bypinching and clamping a periphery of a separator along a joint surfaceof an upper housing and a lower housing being divided up and down. Aninner space of the muffler is partitioned by the separator. An inletopening and an outlet opening which communicates the first and thesecond chambers partitioned by the separator with an exhaust port of theinternal combustion engine and to an outside air respectively aredisposed in the muffler. A cylindrical member having a small hole or aclearance is attached to the inlet opening in the first chamber, and thecylindrical member is provided with an exhaust gas purifying catalyst.(Patent document 9)

Patent document 1: Japanese Laid-Open Patent Application Publication No.06-248939 (refer to paragraphs 0012 and 0014, and FIG. 2)

Patent document 2: Japanese Laid-Open Patent Application Publication No.06-66137 (refer to paragraphs 0010 and 0011, and FIG. 2)

Patent document 3: Japanese Laid-Open Patent Application Publication No.06-33754 (refer to paragraph 0010, and FIG. 1)

Patent document 4: Japanese Laid-Open Patent Application Publication No.07-293231 (refer to paragraphs 0010 and 0012, and FIG. 1 and FIG. 2)

Patent document 5: Japanese Laid-Open Utility Model ApplicationPublication No. 07-40648 (refer to FIG. 3 and FIG. 4)

Patent document 6: Japanese Laid-Open Patent Application Publication No.2002-242666 (refer to paragraphs 0034, 0035 and 0036, and FIG. 1)

Patent document 7: Japanese Laid-Open Patent Application Publication No.10-8942 (refer to paragraphs 0006, 0014 and 0024, and FIG. 1 and FIG. 2)

Patent document 8: Japanese Laid-Open Utility Model ApplicationPublication No. 06-18617 (refer to claims, and FIG. 1 and FIG. 2)

Patent document 9: Japanese Laid-Open Utility Model ApplicationPublication No. 05-21114 (refer to claims, and FIG. 1 and FIG. 2)

However, in a conventional muffler of an engine as shown in FIG. 21, forexample, because the exhaust gas purifier 5 is constituted by thehoneycomb-like stainless steel support body coated with the catalyst forpurifying exhaust gas, there is a problem that the manufacturing processis complicated and that a manufacturing cost is high.

Further, though the exhaust gas receiver 6 which is a component of aconventional improved muffler is formed to the concave shape and aplurality of communicating holes 6 a are bored on the concave surface 6a as shown in FIG. 22, no function for purifying the exhaust gas is notprovided therewith.

The exhaust gas muffler of a 2-stroke engine as described in the patentdocument 1 includes the catalyst carrier. The catalyst carrier is madeby laminating thin metal sheets each having numerous openings with eachsurface of the cloth catalyst. The catalyst carrier is formed into thewaveform shape and the plate side is disposed in parallel with a flowdirection of the exhaust gas. There is a problem that a manufacturingprocess is complicated and that the manufacturing cost is high.

In the exhaust gas muffler of a 2-stroke engine as described in thepatent document 2, because the exhaust gas inlet is not provided withthe heat resistant mesh catalyst and the exhaust gas outlet is notprovided with the heat resistant mesh catalyst, there is a possibilitythat sparks blow out from the exhaust gas outlet when the engine isunder operation.

In the exhaust gas muffler of a 2-stroke engine as described in thepatent document 3, because the exhaust gas inlet is not provided withthe heat resistant mesh catalyst and the exhaust gas outlet is notprovided with the heat resistant mesh catalyst, there is a possibilitythat sparks blow out from the exhaust gas outlet while the engine isunder operation.

In the exhaust gas muffler as described in the patent document 4, theinside of the exhaust gas muffler is not partitioned to the firstexpansion chamber, the second expansion chamber and the third expansionchamber by the partition plate, a muffling effect is not as good asexpected.

In the muffler for an engine as described in the patent document 5,because the cylindrical spark arrestor made of the cylindrical wire meshis retained in a state fixed between the end of the tail pipe and theinner surface of the attaching body of the exhaust gas muffler, it isdifficult to replace the spark arrestor with a new one.

In the exhaust gas muffler for a small engine as described in the patentdocument 6, because the catalyst which has a function of re-burning theunburned gas in the exhaust gas through the oxidation reaction, bycoating the catalyst to the surface of the passage in the honeycombstructure composed of the stainless steel, a manufacturing process iscomplicated and a manufacturing cost is high.

In the exhaust gas muffler for a small engine as described in the patentdocument 7, while the cylindrical oxidation catalyst composed of themetal carrier is disposed as an exhaust gas purifier so as to protrudein the first expansion chamber and the second expansion chamber, thereis a problem that a manufacturing cost of the cylindrical oxidationcatalyst is high. Meanwhile, because between the inner wall panel andthe outer wall panel which form the double wall part, the exhaust gasflows to the outlet opening disposed on the outer wall panel and theouter wall panel is heated thereby, there is a problem that the doublewall part does not have an effect preventing the outer wall of themuffler from being heated.

In the catalyst muffler as described in the patent document 8, becausethe inside of the muffler is not partitioned to the first expansionchamber, the second expansion chamber and the third expansion chamber bythe partition plate, a muffling effect is not good. Further, because themuffler is partitioned to two parts of the body housing and the lidhousing, and the ceramic cloth, the cloth catalyst and the wire meshmade of the stainless steel are stacked in turn and joined to whole theinner surface of each housing, there is a problem that a structure ofthe catalyst in the muffler is complicated and a manufacturing cost ishigh.

In a silencer as described in the patent document 9, because a separatorwhich divides the silencer to two parts is not provided with a catalystfor purifying exhaust gas, there is a problem that a purifying effect onthe exhaust gas is insufficient.

DISCLOSURE OF THE INVENTION

A muffler for a small engine according to one embodiment of the presentinvention includes: a first expansion chamber (12) having an exhaust gasinlet (11) being connected to an exhaust gas outlet of an engine; asecond expansion chamber (15) for exhaust gas being partitioned from thefirst expansion chamber (12) by a partition plate (14) and beingcommunicated with the first expansion chamber (12) through a firstcommunicating hole (13) on the partition plate (14); and a thirdexpansion chamber (18) for the exhaust gas having an exhaust gas outlet(17), being partitioned from the second expansion chamber (15) by thepartition plate (14) and being communicated with the second expansionchamber (15) through a second communicating hole (16) on the partitionplate (14). A first heat resistant mesh catalyst (19) is disposed on theexhaust gas inlet (11). A first exhaust gas purifier (20) composed of aheat resistant knit fabric (20 a) coated with a catalyst for purifyingthe exhaust gas is disposed on the first communicating hole (13) on thepartition plate (14).

Further, in the muffler, the first exhaust gas purifier (20) can becomposed of the heat resistant knit fabric (20 a) coated with thecatalyst for purifying the exhaust gas, supported with a heat resistantcover (20 b) having at least one exhaust gas inlet (20 d).

Further, in the muffler, the first exhaust gas purifier (20) is disposedon an exhaust gas inlet side of the communicating hole (13) on thepartition plate (14), a second heat resistant mesh catalyst (22) and aheat resistant cover having a plurality of exhaust gas outlets (22 a)are disposed on an exhaust gas outlet side thereof, and a third heatresistant mesh catalyst (23) can be disposed replaceably on the exhaustgas outlet (17).

Further, in the muffler, the first exhaust gas purifier (20) can becomposed of the heat resistant knit fabric (20 a) coated with thecatalyst for purifying the exhaust gas, supported with a cover (20 c)made of a heat resistant mesh.

Further, in the muffler, at least an outer wall of the second expansionchamber (15) which is not disposed on a side where the muffler isattached can be composed of a double wall structure of walls (15 a′, 15b).

Further, in the muffler, at least the outer wall of the second expansionchamber (15) which is not disposed on the side where the muffler isattached can be composed of the double wall structure of walls (15 a′,15 b) and an heat insulator 15 c can be packed to the space between thedouble wall structure of walls (15 a′, 15 b).

Further, in the muffler, an exhaust gas receiver (24) is disposed in thefirst expansion chamber (12) disposed opposite the exhaust gas inlet(11). The exhaust gas receiver (24) is connected to the exhaust gasinlet (11) and is provided with an exhaust gas outlet (24 b) disposedopposite the exhaust gas inlet (11). A second exhaust gas purifier (25)which is composed of the heat resistant knit fabric coated with thecatalyst for purifying the exhaust gas is installed on the exhaust gasoutlet (24 b) in the exhaust gas receiver (24). An inclined surface (24a) can be disposed on the exhaust gas outlet (24 b) so that the exhaustgas flows in a direction toward the first exhaust gas purifier (20).

Further, in the muffler, the first heat resistant mesh catalyst (19) canbe made of a SUS310S stainless steel mesh coated with the catalyst forpurifying the exhaust gas.

Further, in the muffler, the second heat resistant mesh catalyst (21)can be made of the SUS310S stainless steel mesh coated with the catalystfor purifying the exhaust gas. The heat resistant cover (22) can be madeof a SUS310S stainless steel sheet. The third heat resistant meshcatalyst (23) can be made of the SUS310S stainless steel mesh coatedwith the catalyst for purifying the exhaust gas.

Further, in the muffler, the exhaust gas receiver (24) can be made ofthe SUS310S stainless steel sheet.

Further, a muffler for a small engine according to another embodiment,includes: a first expansion chamber (12) for exhaust gas having anexhaust gas inlet (11) being connected to an exhaust gas outlet of theengine; a second expansion chamber (15) which is partitioned from thefirst expansion chamber (12) by a partition plate (14); and a thirdexpansion chamber (18) having an exhaust gas outlet (17) beingcommunicated with the second expansion chamber (15) through a secondcommunicating hole (16) on the partition plate (14). A first heatresistant mesh catalyst (19) is disposed on the exhaust gas inlet (11).A convex part (14 b) having at least one first communicating hole (14 a)and protruding toward the first expansion chamber (12) is made in anintegral molding manner. A first exhaust gas purifier (20) composed of aheat resistant knit fabric (20 a) coated with a catalyst for purifyingthe exhaust gas is installed to a concave side of a convex part (14 b)disposed opposite the second expansion chamber (15). A heat resistantcover (22) having the exhaust gas outlet (22 a) is disposed for coveringthe first exhaust gas purifier (20) in a direction from a side of thesecond expansion chamber (15).

A muffler for a small engine according to further another embodiment,includes: a first expansion chamber (12) for exhaust gas having anexhaust gas inlet (11) being connected to the exhaust gas outlet of theengine; a second expansion chamber (15) which is partitioned from thefirst expansion chamber (12) by a partition plate (14); and a thirdexpansion chamber (18) having an exhaust gas outlet (17) beingcommunicated with the second expansion chamber (15) through a secondcommunicating hole (16) on the partition plate (14). A first heatresistant mesh catalyst (19) is disposed on the exhaust gas inlet (11).A convex part (14 d) having an exhaust gas outlet (14 c) and protrudingtoward the second expansion chamber (15) is made in an integral moldingmanner. An exhaust gas purifier (20) composed of a heat resistant knitfabric (20 a) coated with a catalyst for purifying the exhaust gas isinstalled on an exhaust gas inlet side on the side of the firstexpansion chamber (12) of the convex part (14 b). A heat resistant cover(20 b) having at least one exhaust gas outlet (20 d) is disposed forcovering the first exhaust gas purifier (20) from the first expansionchamber (12).

The muffler for a small engine according to further another embodiment,includes: the first expansion chamber (12) for the exhaust gas havingthe exhaust gas inlet (11) being connected to the exhaust gas outlet ofthe engine; and the second expansion chamber (15) being partitioned fromthe first expansion chamber (12) by the partition plate (14) having thefirst communicating hole (13). The first heat resistant mesh catalyst(19) is disposed on the exhaust gas inlet (11). The first exhaust gaspurifier (20) composed of the heat resistant knit fabric (20 a) coatedwith the catalyst for purifying the exhaust gas is disposed on the firstcommunicating hole (13) on the partition plate (14). An outside airsuction pipe (30) is disposed through the second expansion chamber (15).A portion of the outside air suction pipe facing to the first exhaustgas purifier (20) is composed of a double pipe. An end of the outsideair suction pipe penetrates an outer wall and is communicated with anoutside air. A plurality of suction holes (30 b) are bored on an outerpipe of a double pipe (30 a). The other end of the outside air suctionpipe (30) is communicated with the exhaust gas outlet (17) through anexhaust gas guide (33).

In further another embodiment of the muffler for a small engineaccording to the present invention, the exhaust gas guide (33) isprovided with a pipe (34) being communicated with the first expansionchamber (12) of the exhaust gas and having a check valve (35).

In further another embodiment of the muffler for a small engineaccording to the present invention, the muffler includes: the firstexpansion chamber (12) of the exhaust gas having the exhaust gas inlet(11) being connected to the exhaust gas outlet of the engine; and thesecond expansion chamber (15) partitioned from the first expansionchamber (12) by the partition plate (14) having the communicating hole(13). The first heat resistant mesh catalyst (19) is disposed on theexhaust gas inlet (11). The first exhaust gas purifier (20) composed ofthe heat resistant knit fabric (20 a) coated with the catalyst forpurifying the exhaust gas is disposed on the first communicating hole(13) on the partition plate (14). The exhaust gas guide (33) whichcommunicates the second expansion chamber (15) with the exhaust gasoutlet (17), is provided with the pipe (34) being also communicated withthe first expansion chamber (12) of the exhaust gas and having the checkvalve (35).

According to further another embodiment of the muffler for a smallengine of the present invention, in the muffler according to the oneembodiment, another embodiment and further another embodiments of thepresent invention, a concave groove (31) being communicated with thethird expansion chamber (18) at an end and the outside air at the otherend is formed on an outer surface of the muffler, and a groove cover(32) covers the concave groove (31).

According to further another embodiment of the muffler for a smallengine of the present invention, in the muffler according to the oneembodiment, another embodiment and further another embodiments of thepresent invention, an outside air suction pipe (30′) being opened ateach end is fixed along the outer wall of the muffler so as tocommunicate with the exhaust gas outlet (17) at an end and the outsideair at the other end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view according to one embodiment of amuffler for a small engine of the present invention.

FIG. 2 is an exploded perspective view according to the one embodimentof the muffler for a small engine of the present invention.

FIG. 3 is an assembling perspective view according to the one embodimentof the muffler for a small engine of the present invention.

FIG. 4 is a cross-sectional view of the muffler in which a first exhaustgas purifier according to the one embodiment of the muffler for a smallengine of the present invention is modified to another embodiment.

FIG. 5 is an exploded perspective view of the muffler in which the firstexhaust gas purifier according to the one embodiment of the muffler fora small engine of the present invention is modified to the anotherembodiment.

FIG. 6 is an assembling perspective view of the muffler in which thefirst exhaust gas purifier according to the one embodiment of themuffler for a small engine of the present invention is modified to theanother embodiment.

FIG. 7 is a cross-sectional view of a muffler having an outer wallcomposed of a double-wall structure, in a configuration according to theone embodiment of the muffler for a small engine of the presentinvention.

FIG. 8 is a cross-sectional view of the muffler in which a heatinsulator is packed in a space between the double walls of the outerwall, in the configuration as shown in FIG. 7.

FIG. 9 is a cross-sectional view of the muffler in which the firstexhaust gas purifier is modified to another embodiment, in theconfiguration as shown in FIG. 7.

FIG. 10 is a cross-sectional view of the muffler in which a heatinsulator is packed between the double walls of the outer wall, in theconfiguration as shown in FIG. 9.

FIG. 11 is a cross-sectional view according to another embodiment of amuffler for a small engine of the present invention.

FIG. 12 is a cross-sectional view of the muffler in which the firstexhaust gas purifier is modified to another embodiment, in theconfiguration as shown in FIG. 11.

FIG. 13 is a cross-sectional view according to further anotherembodiment of a muffler for a small engine of the present invention.

FIG. 14 is a cross-sectional view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 15 is a cross-sectional view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 16 is a cross-sectional view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 17 is a cross-sectional view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 18 is an exploded perspective view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 19 is an exploded perspective view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 20 is an exploded perspective view according to further anotherembodiment of the muffler for a small engine of the present invention.

FIG. 21 is a cross-sectional view of a conventional muffler for a smallengine.

FIG. 22 is a cross-sectional view of another conventional muffler for asmall engine.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereunder, a detailed description is made referring to the drawings onthe embodiments of the present invention.

FIG. 1 is a cross-sectional view according to one embodiment of amuffler for a small engine of the present invention. FIG. 2 is anexploded perspective view thereof and FIG. 3 is an assemblingperspective view thereof.

The muffler for a small engine according to the one embodiment of thepresent invention includes: a first expansion chamber 12 having anexhaust gas inlet 11 being connected to an exhaust gas outlet of theengine; a second expansion chamber 15 for exhaust gas partitioned fromthe first expansion chamber 12 by a partition plate 14 and communicatedwith the first expansion chamber 12 through a first communicating hole13 on the partition plate 14; and a third expansion chamber 18 for theexhaust gas having an exhaust gas outlet 17, partitioned from the secondexpansion chamber 15 by the partition plate 14 and communicated with thesecond expansion chamber 15 through a second communicating hole 16 onthe partition plate 14. A first heat resistant mesh catalyst 19 isdisposed on the exhaust gas inlet 11. A first exhaust gas purifier 20composed of a heat resistant knit fabric 20 a coated with a catalyst forpurifying the exhaust gas is disposed on the first communicating hole 13on the partition plate 14.

The first exhaust gas purifier 20 is composed of the heat resistant knitfabric 20 a coated with the catalyst for purifying the exhaust gas,supported with a heat resistant cover 20 b having at least one exhaustgas inlet 20 d.

The first exhaust gas purifier 20 is disposed on an exhaust gas inletside of the first communicating hole 13 on the partition plate 14, asecond heat resistant mesh catalyst 21 and a heat resistant cover 22having a plurality of exhaust gas outlets 22 a are disposed on anexhaust gas outlet side thereof, and the third heat resistant meshcatalyst 23 can be disposed replaceably on the exhaust gas outlet 17.

The heat resistant cover 20 b and the heat resistant cover 22 can bemade by press forming a stainless steel sheet and are welded with thepartition plate 14 around the first communicating hole 13.

An outer wall 12 a of the first expansion chamber 12, an outer wall 15 aof the second expansion chamber 15, the partition plate 14, and apartition plate 18 a which is disposed between the partition plate 14and the outer wall 12 a of the first expansion chamber 12 by welding andconstitutes the third expansion chamber 18, are made by forming astainless steel sheet.

Among stainless steel materials, SUS310S stainless steel is preferredfor making the outer wall 12 a of the first expansion chamber 12, theouter wall 15 a of the second expansion chamber 15, the partition plate14, the partition plate 18 a which constitutes the third expansionchamber 18, the heat resistant cover 20 b and the heat resistant cover22 c. If SUS310S stainless steel is used for them, each life can beextended due to the excellent heat resistant and acid resistantproperties.

Further, the first heat resistant mesh catalyst 19, the second heatresistant mesh catalyst 21 and the third heat resistant mesh catalyst 23can be made of a stainless steel wire mesh or a stainless steel sheethaving a number of fine holes bored, coated with a catalyst such as oneor a combination of platinum, rhodium, palladium, etc., for purifyingthe exhaust gas. If the SUS310S stainless steel is used preferably asthe stainless steel material, each life can be extended due to theexcellent heat resistant and acid resistant properties.

Further, the heat resistant knit fabric 20 a is made of a fabric beingknit from a piece of wire or a few pieces of wires of a stainless steeland being folded to a pre-determined thickness, and coated with thecatalyst for purifying the exhaust gas.

A manufacturing process of the heat resistant knit fabric 20 a issimpler and a manufacturing cost grows less, as compared to themanufacturing process and the manufacturing cost of the conventionalstainless steel honeycomb-like substrate.

As shown in FIG. 1, FIG. 2 and FIG. 3, because an inside of the muffleris partitioned into the first expansion chamber 12, the second expansionchamber 15 and the third expansion chamber 18, by the partition plate14, its muffling effect improves. Further, because the first heatresistant mesh catalyst 19 is disposed on the exhaust gas inlet 11,sparks included in the exhaust gas of the engine do not enter themuffler (so called, a spark arrestor effect). Further, because the firstexhaust gas purifier 20 which is disposed on the first communicatinghole 13 bored on the partition plate 14 so as to communicate the firstexpansion chamber 12 with the second expansion chamber 15, is composedof the heat resistant fabric 20 a coated with the catalyst for purifyingthe exhaust gas, the manufacturing process is simpler and amanufacturing cost is reduced.

The second heat resistant mesh catalyst 21 is made of a stainless steelmesh coated with the catalyst for purifying the exhaust gas, and iswelded to the partition plate 14. Further, the third heat resistant meshcatalyst 23 is made of the stainless steel mesh coated with the catalystfor purifying the exhaust gas. If the SUS310S stainless steel is usedpreferably as the stainless steel material, each life can be extendeddue to the excellent heat resistant and acid resistant properties.

FIG. 4 is a cross-sectional view of the muffler in which the firstexhaust gas purifier 20 is modified to another embodiment. FIG. 5 is anexploded perspective view and FIG. 6 is an assembling perspective view.The first exhaust gas purifier 20 is composed of the heat resistant knitfabric 20 a coated with the catalyst for purifying the exhaust gas,supported with the heat resistant cover 20 c made of a heat resistantmesh. The heat resistant mesh can be made by coating a stainless steelmesh with the catalyst for purifying the exhaust gas, and the heatresistant cover 20 c being made as such is welded to the partition plate14. If the SUS310S stainless steel is used preferably as the stainlesssteel material, a life can be extended thereby due to the excellent heatresistant and acid resistant properties.

As described above, because the first exhaust gas purifier 20 isdisposed on an inlet side of the exhaust gas of the first communicatinghole 13 bored through the partition plate 14, and the second heatresistant mesh catalyst 21 and the heat resistant cover 22 having aplurality of the exhaust gas outlets 22 a are disposed on an outletside, the first exhaust gas purifier 20 is heated up fast and atemperature rises. Consequently, the exhaust gas is purified better.Further, because the third heat resistant mesh catalyst 23 is disposedreplaceably on the exhaust gas outlet 17, the sparks can be preventedfrom blowing out, and the third heat resistant mesh 23 can be replacedeasily.

As shown in FIG. 7 and FIG. 9, a wall of the second expansion chamber 15which is not at least a wall of the engine side can be composed of adouble wall structure of walls 15 a′, 15 b.

Further, as shown in FIG. 8 and FIG. 10, the wall of the secondexpansion chamber 15 which is no at least the wall of the engine sidecan be composed of a double wall structure of walls 15 a′, 15 b, and aheat insulator 15 can be packed to a space between the double walls.

By the configuration as described above, the outer wall of the muffleris prevented from being heated up. Further, because the heat insulator15 c is packed into the space between the double walls, an effect forpreventing the outer wall of the muffler from being heated up is high.

According to another embodiment of the present invention, as shown inFIG. 11 and FIG. 12, an exhaust gas receiver 24 can be disposed in thefirst expansion chamber 12 disposed opposite the exhaust gas inlet 11being connected to the exhaust gas outlet of the engine. The exhaust gasreceiver 24 is connected to the exhaust gas inlet 11 and has an exhaustgas outlet 24 b disposed opposite the exhaust gas inlet 11. In thevicinity of the exhaust gas outlet 24 b inside the exhaust gas receiver24, a second exhaust gas purifier 25 composed of the heat resistant knitfabric coated with the catalyst is disposed. An inclined surface 24 a isattached to the exhaust gas outlet 24 b and therefore the exhaust gasflows in a direction toward the first exhaust gas purifier 20.

After installing the second exhaust gas purifier 25 in the exhaust gasreceiver 24, a center portion of the exhaust gas receiver 24 is deformedso as to protrude inward, and the second exhaust gas purifier 25 isfixed so as not to be detached.

By the configuration as described above, because a first exhaust gasexhausted from the engine is received by the exhaust gas receiver 24 andis purified by the second exhaust gas purifier 25 disposed therein, apurification effect on the exhaust gas is better.

Further, because the first heat resistant mesh catalyst 19 is made ofthe SUS310S stainless steel mesh coated with the catalyst for purifyingthe exhaust gas, a life of the first heat resistant mesh catalyst 19 canbe extended due to the excellent heat resistant and acid resistantproperties.

Further, because the second heat resistant mesh catalyst 21 is made ofthe SUS310S stainless steel mesh coated with the catalyst for purifyingthe exhaust gas, the heat resistant cover 22 is made of the SUS310Sstainless steel sheet and the third heat resistant mesh catalyst 23 ismade of the SUS310S stainless steel mesh coated with the catalyst forpurifying the exhaust gas, each life of the second heat resistant meshcatalyst 21, the heat resistant cover 22 and the third heat resistantmesh catalyst 23 can be extended due to the excellent heat resistant andacid resistant properties.

Further, the exhaust gas receiver 24 is made of the SUS310S stainlesssteel sheet, and the second exhaust gas purifier 25 composed of thestainless steel knit fabric coated with the catalyst for purifying theexhaust gas is installed therein. Each life of the exhaust gas receiver24 and the second exhaust gas purifier 25 is extended due to theexcellent heat resistant and acid resistant properties.

According to another embodiment of the muffler for a small engine of thepresent invention, as shown in FIG. 13, a convex part 14 b having atleast one first communicating hole 14 a and protruding toward firstexpansion chamber 12 is made on the partition plate 14 in an integralmolding manner. The first exhaust gas purifier 20 composed of thestainless steel knit fabric coated with the catalyst for purifying theexhaust gas is installed to a concave part on the side of the secondexpansion chamber (15) of the convex part (14 b), and the heat resistantcover 22 having the exhaust gas outlet 22 a covers the first exhaust gaspurifier 20 from the second expansion chamber 15. Consequently, thefirst exhaust gas purifier 20 can be manufactured at a lower cost due toa simpler configuration. The exhaust gas outlet 22 a is disposed so thatthe exhaust gas does not flow in a direction toward the outer wall 15 aof the second expansion chamber 15, but flows along the partition plate14.

According to further another embodiment of a muffler for a small engineof the present invention, as shown in FIG. 14, a convex part 14 d havingan exhaust gas outlet 14 c and protruding toward second expansionchamber 15 is made on the partition plate 14 in an integral moldingmanner. The first exhaust gas purifier 20 composed of the stainlesssteel knit fabric 20 a coated with the catalyst for purifying theexhaust gas is installed to an inlet side of the concave part of theconvex part on the side of the first expansion chamber (12), and theheat resistant cover 20 b having at least one exhaust gas inlet 20 dcovers the first exhaust gas purifier 20 from the first expansionchamber 12. Consequently, the first exhaust gas purifier 20 can bemanufactured at a lower cost due to a simpler configuration. The exhaustgas outlet 14 c is disposed so that the exhaust gas does not flow in adirection toward the outer wall 15 a of the second expansion chamber 15,but flows along the partition plate 14.

In further another embodiment of the muffler for a small engineaccording to the present invention, as shown in FIG. 15, the firstexpansion chamber 12 for the exhaust gas having the exhaust gas inlet 11is connected to the exhaust gas outlet of the engine and the secondexpansion chamber 15 is partitioned from the first expansion chamber 12by the partition plate 14 having the communicating hole 13. The firstheat resistant mesh catalyst 19 is disposed on the exhaust gas inlet 11.The first exhaust gas purifier 20 composed of the heat resistant knitfabric 20 a coated with the catalyst for purifying the exhaust gas isdisposed on the first communicating hole 13 on the partition plate 14.An outside air suction pipe 30 is disposed through the second expansionchamber 15. A portion of the outside air suction pipe 30 disposedopposite the first exhaust gas purifier 20 is composed of a double pipe.An end of the outside air suction pipe penetrates the outer wall and iscommunicated with the outside air. A plurality of suction holes 30 b arebored on an outer pipe of the double pipe 30 a. The other end of theoutside air suction pipe 30 is communicated with the exhaust gas outlet17 through an exhaust gas guide 33.

Meanwhile, in the embodiment as shown in FIG. 15, while the exhaust gaspurifier 20 is composed of the heat resistant knit fabric 20 a,supported with the heat resistant cover 20 c made of the heat resistantmesh, the exhaust gas purifier 20 can be constituted, as shown in FIG.1, by the heat resistant knit fabric 20 a supported with the heatresistant cover 20 b having at least one exhaust gas inlet 20 d.

Because such an outside air suction pipe 30 is disposed, the exhaust gaspassing through the first exhaust gas purifier 20 enters the outer pipe30 a through the suction holes 30 b bored on the outer pipe 30 a of thedouble pipe portion of the outside air suction pipe 30, and flows in adirection toward the exhaust gas outlet 17. Consequently, because theexhaust gas in the outside air suction pipe 30 is suctioned, the outsideair enters the outside air suction pipe 30 from an outside air suctioninlet 30 c at the other end thereof and a temperature of the exhaust gasbeing exhausted from the exhaust gas outlet 17 lowers.

In further another embodiment of the muffler for a small engineaccording to the present invention, as shown in FIG. 16, a pipe 34 isconnected to the exhaust gas guide 33 so that it communicates with theexhaust gas first expansion chamber 12, and a check valve 35 is attachedto the pipe 34.

The check valve 35 can be a butterfly valve as shown in FIG. 16 (b), anda top end portion of the pipe 34 can be formed to a smaller size asshown in FIG. 16 (c).

Accordingly, because the outside air (oxygen) flows into the firstexpansion chamber 12 through the check valve 35 attached to the pipe 34,a burning efficiency of the exhaust gas while the exhaust gas in thefirst expansion chamber 12 being burned in the first exhaust gaspurifier 20 is high, and further, because part of the exhaust gasre-circulates into the first expansion chamber 12 and is re-burned inthe first exhaust gas purifier 20, a purifying effect on the exhaust gasis good.

In further another embodiment of the muffler for a small engineaccording to the present invention, as shown in FIG. 17, the firstexpansion chamber 12 of the exhaust gas having the exhaust gas inlet 11is connected to the exhaust gas outlet of the engine and the secondexpansion chamber 15 is partitioned from the first expansion chamber 12through the partition plate 14 having the communicating hole 13. Thefirst heat resistant mesh catalyst 19 is disposed on the exhaust gasinlet 11. The first exhaust gas purifier 20 composed of the heatresistant knit fabric 20 a coated with the catalyst for purifying theexhaust gas is disposed on the first communicating hole 13 on thepartition plate 14. The exhaust gas guide 33 which communicates thesecond expansion chamber 15 with the exhaust gas outlet 17, is providedwith the pipe 34 which is also communicated with the first expansionchamber 12 of the exhaust gas and has the check valve 35.

Accordingly, because part of the exhaust gas in the second expansionchamber 15 re-enters the first expansion chamber 12 through the pipe 34and the check valve 35, and is re-burned in the first expansion chamber20, a purification effect on the exhaust gas is good.

In further another embodiment of the muffler for a small engineaccording to the present invention, as shown in FIG. 18, a concavegroove being communicated with the third expansion chamber 18 (refer toFIG. 1) at an end and with the outside air at the other end is formed onan outer surface of the muffler, and a groove cover 32 covers theconcave groove 31. The exhaust gas is exhausted from the third expansionchamber 18 through an exhaust gas outlet 17. The outside air enters thethird expansion chamber 18 through the concave groove 31 formed on theouter wall of the muffler following the exhaust gas being exhausted.Therefore, temperature of the exhaust gas being exhausted from theexhaust gas outlet 17 lowers. Here, as shown in FIG. 19, the groovecover which covers the concave groove 31 can be made in one memberincluding a lattice member 28′ which covers the exhaust gas outlet 17 ofthe third expansion chamber 18 and a groove cover 32′ which covers theconcave groove 31.

In further another embodiment of the muffler for a small engineaccording to the present invention, as shown in FIG. 20, an outside airsuction pipe 30′ being opened at each end is fixed along the outer wallof the muffler so as to communicate with the exhaust gas outlet 17 at anend and the outside air at the other end. Because the outside air entersthe third expansion chamber 18 through the other end of the outside airsuction pipe 30′ following the exhaust gas which is exhausted from thethird expansion chamber 18 (refer to FIG. 1) through the exhaust gasoutlet 17, temperature of the exhaust gas being exhausted from theexhaust gas outlet 17 lowers. The outside air suction pipe 30′ can befixed along the outer wall of the muffler by means such as welding, etc.

Further, as shown in FIG. 1, FIG. 3, FIG. 4, FIG. 6 and FIG. 11 to FIG.17, each end portion of the outer walls 12 a, 15 a, and the partitionplate 14 is fixed by clamping.

Meanwhile, as shown in FIG. 7 to FIG. 10, each end portion of thedouble-walls 12 a, 12 b, the partition plate 15 and the double-walls 15a′, 15 b forming the second expansion chamber 15 is fixed by clamping.

The numeral ‘26’ is, as indicated in FIG. 1 to FIG. 6 and FIG. 11 toFIG. 20, a pipe member which is disposed on a position between the outerwall 12 a forming the first expansion chamber 12 and the outer wall 15 aforming the second expansion chamber 15, and in which a bolt 27 forfixing the muffler to the engine is inserted. The numeral ‘28’, asindicated in FIG. 1 to FIG. 6 and FIG. 11 to FIG. 20, is a latticemember which is attached replaceably to the outer wall 12 a of themuffler using an attaching screw. The third heat resistant mesh catalyst23 can be replaced by detaching the lattice member 28.

1. A muffler for a small engine, comprising: a first expansion chamberof exhaust gas having an exhaust gas inlet being connected to an exhaustgas outlet of the engine; a second expansion chamber of the exhaust gasbeing partitioned from the first expansion chamber by a partition plateand being communicated with the first expansion chamber through a firstcommunicating hole through the partition plate; a third expansionchamber of the exhaust gas having an exhaust gas outlet and beingpartitioned from the second expansion chamber by the partition plate andbeing communicated with the second expansion chamber through a secondcommunicating hole through the partition plate, a first heat resistantmesh catalyst disposed at the exhaust gas inlet; and a first exhaust gaspurifier composed of a knit fabric coated with a catalyst for purifyingthe exhaust gas and disposed at the first communicating hole.
 2. Themuffler for a small engine according to claim 1, further comprising: aheat resistant cover having at least one exhaust gas inlet forsupporting the knit fabric.
 3. The muffler for a small engine accordingto claim 1, further comprising: a second heat resistant mesh catalystand a heat resistant cover having a plurality of exhaust gas outletsdisposed on an outlet side of the exhaust gas; and a third heatresistant mesh catalyst disposed replaceably on the exhaust gas outletwherein the first exhaust gas purifier is disposed on an exhaust gasinlet side of the first communicating hole through the partition plate.4. The muffler for a small engine according to claim 1, furthercomprising: a heat resistant cover made of a heat resistant mesh forsupporting the knit fabric.
 5. The muffler for a small engine accordingto claim 1, wherein at least an outer wall of the second expansionchamber which is not disposed on a side where the muffler is attached isconstituted by a double-wall structure of walls.
 6. The muffler for asmall engine according to claim 1, wherein the outer wall of the secondexpansion chamber which is not at least the wall of the engine side isconstituted by the double-wall structure of walls and a heat insulatoris packed into a space between the double walls.
 7. The muffler for asmall engine according to claim 1, further comprising: an exhaust gasreceiver disposed inside the first expansion chamber disposed oppositethe exhaust gas inlet, being connected to the exhaust gas inlet andhaving an exhaust gas outlet opposite the exhaust gas inlet; and asecond exhaust gas purifier composed of the heat resistant knit fabriccoated with the catalyst for purifying the exhaust gas, being installedin a vicinity of the exhaust gas outlet inside the exhaust gas receiver;and an inclined surface formed on the exhaust gas outlet so as to flowthe exhaust gas in a direction toward the first exhaust gas purifier. 8.The muffler for a small engine according to claim 1, wherein the firstheat resistant mesh catalyst is made of a SUS310S stainless steel meshcoated with the catalyst.
 9. The muffler for a small engine according toclaim 3, wherein the second heat resistant mesh catalyst is made of theSUS310S stainless steel mesh coated with the catalyst for purifying theexhaust gas, the heat resistant cover is made of a SUS310S stainlesssteel sheet, and the third heat resistant mesh catalyst is made of theSUS310S stainless steel mesh coated with the catalyst for purifying theexhaust gas.
 10. The muffler for a small engine according to claim 7,wherein the exhaust gas receiver is made of the SUS310S stainless steelsheet.
 11. A muffler for a small engine, comprising: a first expansionchamber of the exhaust gas having an exhaust gas inlet being connectedto an exhaust gas outlet of the engine; a second expansion chamber beingpartitioned from the first expansion chamber by a partition plate; athird expansion chamber having an exhaust gas outlet being communicatedwith the second expansion chamber through a second communicating hole onthe partition plate, a first heat resistant mesh catalyst disposed atthe exhaust gas inlet; a convex part having at least one firstcommunicating hole and protruding toward the first expansion chamber,the convex part made in an integrally molding manner with the partitionplate; a first exhaust gas purifier composed of a heat resistant knitfabric coated with the catalyst for purifying the exhaust gas installedon a concave part on the side of the second expansion chamber of theconvex part; and a heat resistant cover having an exhaust gas outletdisposed for covering the first exhaust gas purifier in a direction fromthe second expansion chamber.
 12. A muffler for a small engine,comprising: a first expansion chamber of the exhaust gas having anexhaust gas inlet being connected to an exhaust gas outlet of theengine; a second expansion chamber which is partitioned from the firstexpansion chamber by a partition plate; a third expansion chamber havingan exhaust gas outlet being communicated with the second expansionchamber through a second communicating hole on the partition plate; afirst heat resistant mesh catalyst disposed on the exhaust gas inlet; aconvex part having an exhaust gas outlet and protruding toward thesecond expansion chamber, the convex part made in an integrally moldingmanner with the partition plate; a heat resistant knit fabric coatedwith a catalyst for purifying the exhaust gas installed on an exhaustgas inlet side on the side of the first expansion chamber of the convexpart; and a heat resistant cover having an exhaust gas outlet disposedfor covering the first exhaust gas purifier the first expansion chamber.13. A muffler for a small engine, comprising: a first expansion chamberfor the exhaust gas having an exhaust gas inlet being connected to anexhaust gas outlet of the engine; a second expansion chamber beingpartitioned from the first expansion chamber by a partition plate havinga communicating hole; a first heat resistant mesh catalyst disposed onthe exhaust gas inlet; a first exhaust gas purifier composed of a heatresistant knit fabric coated with a catalyst for purifying the exhaustgas is disposed on the first communicating hole on the partition plate;and an outside air suction pipe disposed through the second expansionchamber, a portion of the outside air suction pipe disposed opposite thefirst exhaust gas purifier and composed of a double pipe, an end of theoutside air suction pipe bored through the outer wall and communicatingwith an outside air, wherein a plurality of suction holes are boredthrough an outer pipe of the double pipe and the other end of theoutside air suction pipe communicates with an exhaust gas outlet throughan exhaust gas guide.
 14. The muffler for a small engine according toclaim 13, wherein the exhaust gas pipe is provided with a pipe having acheck valve and being communicated with the first expansion chamber ofthe exhaust gas.
 15. A muffler for a small engine, comprising: a firstexpansion chamber of exhaust gas having an exhaust gas inlet beingconnected to an exhaust gas outlet of the engine; a second expansionchamber partitioned from the first expansion chamber by a partitionplate having a communicating hole; a first heat resistant mesh catalystdisposed on the exhaust gas inlet; a first exhaust gas purifier composedof a heat resistant knit fabric coated with a catalyst for purifying theexhaust gas disposed on a first communicating hole on the partitionplate; and an exhaust gas pipe communicating the second expansionchamber with an exhaust gas outlet provided with a pipe beingcommunicated with the first expansion chamber of the exhaust gas andhaving a check valve.
 16. The muffler for a small engine according toclaim 1, wherein a concave groove which is communicated with the thirdexpansion chamber at an end and with the outside air at the other end isformed on an outer surface of the muffler, and a groove cover covers theconcave groove.
 17. The muffler for a small engine according to claim 1,wherein an outside air suction pipe being opened at each end is fixedalong the outer wall of the muffler so as to communicate with theexhaust gas outlet at an end and with the outside air at the other end.